Etoricoxib decreases mouse subchondral bone mass and biomechanical properties in early osteoarthritis

Background Etoricoxib, a selective Cyclooxygenase-2 (COX-2) inhibitor, is commonly used in osteoarthritis (OA) for pain relief. The purpose of our study was to investigate the effects of Etoricoxib on mouse subchondral bone in early OA. Methods OA was induced via destabilization of the medial meniscus (DMM) in C57BL/6J mice. After surgery, the mice were randomly and equally divided into five groups: a sham-operated control group (Sham group), an osteoarthritis (OA) group (DMM group), an OA treated with Etoricoxib 5mg/kg (DMM+E5) group, an OA treated with Etoricoxib 10mg/kg (DMM+E10) group, and an OA treated with Etoricoxib 20mg/kg (DMM+E20) group. Mice in the Sham group and DMM group were injected with a similar dose of vehicle (40% ethyl alcohol–saline solution). Four weeks after treatment, mice were euthanized. Micro computed tomography (Mirco-CT) analysis, Safranin O-Fast Green staining, hematoxylin and eosin (HE) staining were performed to evaluate morphological and structural changes. In addition, atomic force microscopy (AFM) analysis was performed to evaluate changes in the elastic modulus. Furthermore, changes in microstructure were detected by scanning electron microscopy (SEM). Results Etoricoxib inhibited osteophyte formation in the subchondral bone. However, it also reduced the bone volume fraction (BV/TV), lowered trabecular thickness (Tb.Th), and more microfractures and pores were observed in the subchondral bone. Moreover, Etoricoxib reduced the elastic modulus of subchondral bone. Furthermore, exposure to Etoricoxib further increased the empty/total osteocyte ratio of the subchondral bone. In cartilage and synovium, Etoricoxib did not significantly change the Osteoarthritis Research Society International (OARSI) score, the modified Mankin score, and the synovialitis-score versus the DMM group. Conclusion Although Etoricoxib can relieve the pain induced by OA, it can also change microstructures and biomechanical properties of the subchondral bone at the early stage of OA, cause osteoporotic changes in subchondral bone structure, increase the risk of fragile fracture of subchondral bone.